This application relates to a transparent article having a metallic flake appearance and having a high impact performance at low temperature conditions. Specifically, this application relates to compositions that possess low temperature ductility comprising metal oxide-coated or metal-coated glass platelets dispersed within a transparent polysiloxane-polycarbonate copolymer resin matrix, methods to make such compositions and articles derived from these compositions and methods, which articles possess low temperature ductility.
As thermoplastics become increasingly important in the marketplace, producers have sought to differentiate their products by making them more visually exciting to the customer. One desirable look for thermoplastics is a metal flake appearance. This appearance can be described as the look one could imagine if small pieces of very shiny metal were dispersed in molten glass, and the glass subsequently cooled. The flakes have a bright metallic glint, but one can perceive clear spaces between the flakes such that these regions of the article are completely transparent.
United States Statutory Invention Registration, US H1975 H, describes a thermoplastic article having a metallic flake appearance and a means of producing a thermoplastic article having a metallic flake appearance by extruding a thermoplastic polymer together with an amount of metal-oxide coated glass platelets effective to provide a metal flake appearance.
Previous thermoplastic compositions with metal oxide-coated glass platelets possessed poor impact performance (i.e., resistance to shattering upon impact), especially when subjected to low temperature conditions. The cause of this poor impact performance was thought to be due to an interaction of the metal oxide-coated platelet with the thermoplastic resin. It was surmised that the metal oxide-coated platelets served as stress concentrators in an impact situation, leading to easy breakage of an article containing them. Even the use of a high impact strength thermoplastic resin, such as a polycarbonate resin, did not eliminate the breakage issue. The impact problem becomes more severe as the temperature of the surroundings is reduced and as the amount of metal platelets is increased.
The reduction of impact strength of thermoplastic articles, which contain metal oxide coated platelets adversely impacts their market acceptance and commercial growth. For example, the use of articles with a metal flake appearance in many automotive interior applications is substantially limited because automotive producers require that only high impact strength thermoplastics be used in automotive interiors to prevent shattered plastic from causing injury to passengers in an automobile accident. The loss of impact strength for articles with a metal-oxide coated platelets also limits their use in many outdoor applications, for example outdoor postal boxes, where low temperature impact performance is critical.
The compositions and methods according to the present invention provide articles with both the desirable metal flake appearance and the high impact performance especially in low temperature environments.